Estimating Pasture Intake

Whether on a seasonal or continual basis, pasture is often the primary feed in many diets. Pasture consumption must be determined to correctly assess its contribution of nutrients to the diet. Unlike barn-fed feeds that can be weighed, pasture intake must be estimated. The understanding of a few basic concepts (Dry matter Intake and As Sampled vs. Dry Matter) will enable you to simply calculate pasture intake.

The first step is to determine total dry matter intake. Total intake is based on body weight, level of activity, reproductive status and growth stage. Intake values are located in Dry Matter Intake Table. Combining this information with the known consumption of other feeds, enables the calculation of pasture intake by difference.

Examples

A. Pasture as Sole Feed

An 1100 lb. horse is on a maintenance diet. It spends the majority of it’s time on pasture and is ridden occasionally on weekends. It’s summer, and no hay or grain is fed in the barn. Pasture is the sole feed. It’s lush and 20% dry matter (80% moisture). From the Dry Matter Intake Table, intake is estimated at 1.6% of body weight.

1. Calculate Lbs. of dry matter intake.
Lbs. dry matter intake = body weight x (%Dry Matter Intake/100)
Lbs. dry matter intake = 1100 x (1.6/100) = 17.6 Lbs.
2. Calculate Lbs. of pasture consumed, as fed.
Lbs. consumed, as fed = Lbs. Dry Matter Intake / (dry matter %/100)
Lbs. consumed, as fed = 17.6 / (20/100) = 88 Lbs.

Thus, to meet it’s daily need for dry matter, this horse will need to consume 17.6 Lbs. of dry matter, which converts to 88 lbs. of pasture as fed.

B.  Pasture as one of several feeds.

An 1100 lb. horse under light work is fed 7 lbs. of hay and 5 lbs. of grain in the barn and has open access to pasture. From the Dry Matter Intake Table, expected intake is 1.8% of body weight. The hay and the grain are both 90% dry matter and the pasture is 20% dry matter.
1. Calculate Lbs. of dry matter intake.
Lbs. dry matter intake = body weight x (% Dry Matter Intake/100)
Lbs. dry matter intake = 1100 x (1.8/100) = 19.8 Lbs.
2. Calculate the Lbs. of dry matter consumed from hay and grain.
Lbs. dry matter consumed = Lbs. as fed x (dry matter %/100)
Feed Lbs., as fed x Dry matter % = Lbs. Dry Matter
Hay         7 90/100         6.3
Grain         5 90/100         4.5
Total       10.8
3. Estimate Lbs. of pasture dry matter consumed.
Predicted total dry matter intake    19.8
Calculated amounts of other feeds   -10.8
Estimated pasture dry matter intake      9.0
4. Estimate Lbs. of pasture consumed, as fed.
Lbs. of pasture, as fed = Lbs. of pasture dry matter / (dry matter %/100)
Lbs. of pasture, as fed = 9.0 / (20/100) = 45 Lbs.

In summary, pasture intakes are predicted estimates and will vary depending upon the quality, quantity and availability of pasture, as well as the individual horse. Monitor the body condition of horses consuming pasture as the primary forage. If they begin to lose weight, it’s good evidence that they are not consuming enough or that nutrient quality is deficient. Consult with your nutrition professional and adjust the ration to insure that daily nutrient needs are met.